--- p/gpc-common.c.orig	Wed May 15 05:45:08 2002
+++ p/gpc-common.c	Sat Jun 15 21:05:04 2002
@@ -1319,6 +1319,12 @@
   /* Handle IN_EXPR, reverse the arguments for expr.c. */
   if (code == IN_EXPR)
     {
+      if (TREE_CODE (TREE_TYPE (exp2)) != SET_TYPE)
+        {
+          error ("right operand to `in' must be a set");
+          return error_mark_node;
+        }
+
       if (TREE_CODE (TREE_TYPE (TREE_TYPE (exp2))) == VOID_TYPE)
         {
           warning ("`... in []' (empty set) is always `False'");